Microporous composite sheet material

Abstract

A moisture vapor permeable, water impermeable composite sheet material is provided which is suitable for use as a housewrap material, and is also useful for other applications such as tarpaulins, or as covers for automobile, boats, patio furniture or the like. The composite sheet material includes a nonwoven substrate and an extrusion-coated polyolefin film layer overlying one surface of the substrate. The nonwoven substrate is comprised of polymeric fibers randomly disposed and bonded to one another to form a high tenacity nonwoven web. The nonwoven substrate has a grab tensile strength of at least 178 Newtons (40 pounds) in at least one of the machine direction (MD) or the cross-machine direction (CD). The extrusion coated polyolefin film layer is intimately bonded to the nonwoven substrate. The film layer has micropores formed therein to impart to the composite sheet material a moisture vapor transmission rate (MVTR) of at least 35 g/m 2 /24 hr. at 50% relative humidity and 23° C. and a hydrostatic head of at least 55 cm. In one embodiment, the nonwoven substrate comprises a spunbonded nonwoven fabric formed of randomly disposed substantially continuous polypropylene filaments. The spunbonded nonwoven fabric is an area bonded fabric in which the filaments are bonded to one another throughout the fabric at locations where the randomly disposed filaments overlie or cross one another.

1. A moisture vapor permeable, water impermeable composite sheet material having strength and barrier properties making it suitable for use as a housewrap, comprising
 an area bonded, spunbond nonwoven substrate comprising polymeric filaments randomly disposed and bonded to one another at locations where the randomly disposed filaments overlie or cross one another; 
 a polyolefin film extrusion coating layer extending continuously over a surface of the nonwoven substrate and intimately bonded thereto, the extrusion coating layer defining an outer surface of the composite sheet material, and 
 the film layer having micropores formed therein by stretching to impart to the composite sheet material a hydrostatic head of at least 100 cm, and a moisture vapor transmission rate (MVTR) of at least 35 g/m 2/24  hr, at 50% relative humidity and 23° C., and 
 wherein the nonwoven substrate has a grab tensile strength of at least 178 Newtons in at least one of the machine direction (MD) or the cross-machine direction (CD). 
 
     
     
       2. The composite sheet material according to  claim 1 , wherein the composite sheet material has been incrementally stretched in at least one of the MD or CD to form incrementally stretched zones separated by zones of substantially unstretched or less stretched material. 
     
     
       3. The composite sheet material according to  claim 1 , wherein the nonwoven substrate has basis weight of at least 50 g/m 2  and a grab tensile strength in both the machine direction (MD) and cross-machine direction (CD) of at least 178 Newtons. 
     
     
       4. The composite sheet material according to  claim 1 , wherein the nonwoven substrate is formed from substantially continuous cold-drawn, molecularly oriented filaments. 
     
     
       5. The composite sheet material according to  claim 3 , wherein the nonwoven substrate comprises a spunbond nonwoven fabric formed of randomly disposed substantially continuous cold-drawn, molecularly oriented polypropylene filaments. 
     
     
       6. The composite sheet material according to  claim 3 , wherein the film layer has a basis weight of at least 25 g/m 2 . 
     
     
       7. The composite sheet material according to  claim 1 , wherein the composite sheet material has a Gurley porosity of at least 400 seconds. 
     
     
       8. The composite sheet material according to  claim 1 , wherein the composite sheet material has a basis weight of from 60 to 140 g/m 2 . 
     
     
       9. The composite sheet material according to  claim 8 , wherein the composite sheet material has a basis weight of from 80 to 110 g/m 2 . 
     
     
       10. The composite sheet material according to  claim 1 , wherein the composite sheet material has an air leakage rate of less than 0.015 L/(s·m 2 ). 
     
     
       11. The composite sheet material according to  claim 1 , wherein the film layer comprises at least 40% by weight inorganic filler, and the composite sheet material has been subjected to stretching in both the CD and MD by incremental stretching to impart to the composite sheet material a moisture vapor transmission rate (MVTR) of at least 100 g/m 2 /24 hr, at 50% relative humidity and 23° C.